1. Field of the Invention
This invention relates to improvements in an electric tilt or telescopic steering apparatus for a vehicle, and more particularly to an electric steering apparatus in which occurrence of back-lash of a position adjusting portion can be effectively prevented.
2. Related Background Art
An electric steering apparatus is such that the position of a steering wheel can be adjusted by the drive force of an electric motor, and there are known an electric steering apparatus in which a steering wheel tilts and an electric steering apparatus in which a steering wheel moves axially (telescopically). In any of these conventional types, a screw shaft is connected to an upper column and a nut member threadably engaged with the screw shaft is supported by a bracket and is rotated by an electric motor to thereby move the screw shaft in the axial direction and adjust the position of the steering wheel.
In the conventional tilt type electric steering apparatus, in addition to the screw shaft and a hinge portion, a speed reduction mechanism and a mechanism for changing the direction of transmission of the drive force (a gear, etc.) are disposed in the route path for transmitting the drive force of the electric motor to the upper, and back-lash exists in each of these portions. Individual back-lash in each portion is small, but the cumulative effect may be great, whereby back-lash appears in the direction of tilt of the steering wheel. This spoils the sense of rigidity, and has led to the problem that during driving, stability of manipulation is lacking and annoying vibrations and noise occur.
On the other hand, in the telescopic type electric steering apparatus, the hinge portion is absent but the speed reduction mechanism and the mechanism for changing the direction of transmission exhibit back-lash, as in the tilt type electric steering apparatus. One such an electric steering apparatus is shown, for example, in Japanese Laid-Open patent application Ser. No. 230861/1984, but this apparatus has disadvantages in that the number of parts is great and the structure is complex and that the presence of two fulcrums for a link leads to great back-lash and cumbersomeness of operation.
In the conventional tilt apparatus, the upper column pivotally moves and thus, the locus of movement of a particular point of the upper column describes an arc. If a nut is directly coupled to the upper column without the use of a link, the direction of movement of the nut member which provides a screw shaft does not coincide with the direction of movement of the nut member controlled by the upper column. Therefore, an unreasonable force is applied to the portion at which the nut member is fixed to a fixed bracket, the threadably engaged portions of the nut member and the screw shaft, and the connecting portion between the screw shaft and the upper column, whereby smooth tilt is difficult.